It is normal practice in large irrigation systems for sugar cane fields, row crops, vineyards, orchards, and the like to provide so-called purge valves at the terminal ends of the lateral irrigation pipes. These valves permit water to flush from the ends of the laterals under low pressure conditions. When the pressure in the irrigation system reaches a given value or exceeds this value, these purge valves automatically close so that normal irrigation operations can take place.
By using purge valves, the lines are cleaned of sediment, and the like and water is simply drained from the irrigation system when not is use. In an effort to provide the desired action of dripping or draining of water under low pressure and yet positive closure under high pressure, many sophisticated designs have been proposed and some of these have actually been placed in operation. Typical of such valves are spring loaded ball type check valves or flap valves with guiding stems.
A major factor for consideration with respect to purge type valves at the end of irrigation lines is the actual expense in manufacturing and making available such valves. A further important consideration is reliability. In actuality, the simpler the design of the valve the more likelihood of meeting the foregoing considerations. Thus, if an extremely simple valve structure can be provided, its manufacturing expense is substantially reduced. Moreover, as a general rule, the simpler the valve structure (less moving parts or components) the more reliable will it be.